Protective system



May 10, 1938.

J. w. MCNAIRY 2,117,196

PROTECTIVE SYSTEM Filed Aug. 20, 1957 Inventor: Jacob W. Mc Nairy,

His Attorney.

Patented May 10, 1938 PROTECTIVE SYSTEM Jacob W. McNairy, Erie, Pa., assignor to General Electric Company, a corporation of New York 7 Application August 20, 1937, Serial No. 160,102

4 Claims. (01. 172-179) My invention relates to protective systems for electric motors, more particularly to systems for protecting a plurality of electric traction motors against wheel slippage and has for its object a 5 simple and reliable protective system of this type.

In the operation of a plurality of electric motors separately connected to the driving axles of a vehicle one pair of wheels connected to an axle sometimes slips on the track, especially when electric locomotive.

Referring to the drawing, I have shown my invention in one form as applied to series connected motors l0 and H of the single-phase commutator type. The motors are energized from a trolley wire l2, supplied with single-phase alternating current, energy being taken off through a trolley l3 and a transformer 54. By means of a suitable manually operated controller I5, which may be a drum controller, the supply conductor [6 leading to one side of the motor circuit is connected to a selected tap of suitable voltage on the secondary winding of the transformer l4 so as to control the speed of the motors, the other side of the motor circuit being connected through a supply conductor H to one side of the transformer sec ondary winding.

For the protection of the motors against wheel slippage I have provided a relay switch l8 which any inequality in the voltage of the two motors.

Furthermore the coils l9 and 20 are in reality current coils having comparatively few turns as compared with the windings 22 and 24. Thus under normal conditions there is very little voltage drop across the coils l9 and 20 and the current that flows through them is the exciting cur rent for the windings 22 and 24. In order to increase this exciting current somewhat the core 23 may be provided with an air gap 26.

10 rapid acceleration is attempted under heavy load is normally closed and which is operated upon 10 conditions. When this slipping occurs the motor the occurrence of wheel slippage by the diiferenor motors connected to the slipping axle accelertial effect of the two coils l9 and 20. These two ate to a higher speed than the other motors and coils are connected so as to be responsive respecmay reach a speed causing damage to the motor tively to the voltages of its two motors by conon account of the resulting high mechanical nection across similar portions of the motor cir-- 15 stresses and fiashover at the commutator, cuits, or as shown across the armature of the In carrying out my invention I provide protectwo motors. Each coil has one terminal contive means in which the effect of a difference in nec d to he p n w n h mo r armathe voltages of the motor is increased whereby tllr h Other terminal f the 011 9 l ads the relay is ver sensitive. The .device furtherhro h a win 22 on a magnet core 3 n more is arranged to operate and disconnect the thence to the conductor Hi. In a similar manmotor in the event that it becomes partially dishe the ot er ter al of the co 20 leads abled. Thus an indication is given of this condithroug t W d 24 n the Core 23 t0 t ntion of the protective equipment so that it may be duct The tW windings 22 and 24 are n r repaired and be ready to function to rotect the mutually inductive relation with each other. H motor in the event of wheel slippage, The two coils l9 and 20 are electrically coh- In one form of my invention I provide a reactnected so that under normal operating conditions ance, functioning as an autotransformer, which the two coils opp and neutralize each O is connected across the motor circuit, its winding Preferably y a of identical Construction being divided into two sections in circuit with ing h same number f turns and therefore which are connected tw relay 11 acting i 0pactly neutralize each other under normal balance position to each ther Th midpoint b t motor voltage conditions so that no lifting force the relay coils is connected to the midpoint beis pp d the armature 25 0f the relay tween the motors. With this arrangement a doutuelly, as wn n the w n the i s are pble diiferential effect is obtained by reason of the p y Woundo mutually inductive relation of the two sections of The magnetic C 23 and the windings 22 and the winding whereby the sensitivity of the device 24 av DPODOIlJiOHS Suitable or an auto-transis increased, while if one or the other of the relay former which may be connected p rman nt y coil circuits is disabled the relay is operated imacross the motor pp y Circuit H tOIS l5 and U di t by th other l H, the two windings being so connected that their 10 For a more complete understanding of my inmagnetic effects are cumulative. Moreover the vention reference Shouid be had t t accomtwo windings are identical in construction havpanying drawing a single figure of which is a diaing the same number of turns. Preferably taps grammatic representation of my invention as apare provided 011 one Or both windings for adju tplied to an electrically operated vehicle such as an ment of the number of turns to correspond With In the event of slippage of the wheels driven by one of the motors the particular relay coil l9 or 29 connected across that motor has its energization increased by the increased voltage, i. e. counter E. M. F., of the motor by reason of the increased speed of the motor this effect being substantially proportional to the increasing speed of the motor. For example, if the wheels driven by the motor ll slip, the speed of the motor ll increases and its resulting increased voltage is applied to the winding 24- and the coil 2 with resulting increase in current in this circuit. At the same time, by reason of the mutual inductive relation between the winding 24 and the winding 22, the current through the winding 22 and the coil [9 is reduced. Neglecting the energy losses in the autotransformer, the reduction in current in the coil I9 is approximately the same in amperes as the increase in the current in the coil 20. In other words, the Winding 24 induces a voltage in the winding 22, which voltage reduces the current in the winding 22 and the coil 19. If the voltage of the motor H is increased sufficiently with respect to the voltage of the motor Hi, the current in the coil I9 is reversed so that the two coils become accumulative and both act to operate the armature 25 of the relay.

It will thus be observed that the autotransformer gives increased sensitivity in that an increase in current in one relay coil is accompanied by a corresponding decrease in current in the other coil with therefore a double differential current effect available for the operation of the relay. It will be further observed that the relay coils may be constructed to give great sensitivity in their response because under normal operation with balanced currents. in the coil circuits, the two coils neutralize each other, the relay therefore being unexcited.

In the event of damage to either one of the circuits of the coils l9 and 20 resulting in an open circuit in the coil or any other part of the circuit it will be observed that the other one of the two coils will immediately open the relay [8 to deenergize the motor. In fact in the event of such an open circuit the current in the remaining coil increases to about double its previous value because that coil must then carry the full excitation current for the core 23. This assures operation of the relay by the remaining coil.

When the relay opens, it is latched in the open position by a spring biased latch 28 until the controller I is thrown back to the off position to bridge the terminals 29 and thereby energize a magnet 30 which retracts the latch 28 and allows the relay switch l8 to close.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A protective system for electric motors connected for energization in circuit with each other, comprising a relay for controlling the circuit of said motors, a pair of operating coils for said relay, a pair of windings in inductive relation to each other, and connections connecting each of said relay coils in circuit with one of said windings across at least a portion of the circuit of one of said motors so that said windings are energized accumulatively and said relay coils in opposition to each other.

2. A protective system for electric motors connected for energization in circuit with each other, comprising a relay for controlling the circuit of said motors, a pair of operating coils for said relay, a magnet core, a pair of windings on said core, and connections connecting each of said relay coils in circuit with one of said windings across at least a portion of the circuit of one of said motors so that said windings are energized accumulatively and said relay coils in opposition to each other.

3. A protective system for an electric vehicle provided with a pair of driving axles and a pair of electric motors separately connected to drive said axles, said motors being electrically connected for energization in circuit with each other, comprising a relay for controlling the circuit of said motors, a pair of operating coils for said relay, a pair of windings in inductive relation to each other, and connections connecting each of said relay coils in circuit with one of said windings across at least a portion of the circuit of one of said motors so that said windings are energized accumulatively and said relay coils in opposition to each other in accordance with the respective voltages of said motors.

4. A protective system for an electric vehicle provided with a pair of driving axles and a pair of electric motors separately connected to drive said axles, said motors being electrically connected for energization in series with each other, comprising means for applying a variable voltage to said motors to accelerate said motors, a relay for controlling the circuit of said motors, a pair of operating coils for said relay, a magnet core, a pair of windings on said core and connectionsconnecting each of said relay coils in a circuit with one of said core windings across one of said motors so that said windings are energized accumulatively and said relay coils in opposition to each other.

JACOB W. MCNAIRY. 

